US10801083B2 - Method for melting metal material in a melting plant and relative melting plant - Google Patents

Method for melting metal material in a melting plant and relative melting plant Download PDF

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US10801083B2
US10801083B2 US14/786,152 US201414786152A US10801083B2 US 10801083 B2 US10801083 B2 US 10801083B2 US 201414786152 A US201414786152 A US 201414786152A US 10801083 B2 US10801083 B2 US 10801083B2
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metal material
loading
shell
melting
substep
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US20160076114A1 (en
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Bernard Villemin
Uwe WILHELM
Thomas Narholz
Enrico Riga
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Danieli and C Officine Meccaniche SpA
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Danieli and C Officine Meccaniche SpA
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/527—Charging of the electric furnace
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/56—Manufacture of steel by other methods
    • C21C5/562—Manufacture of steel by other methods starting from scrap
    • C21C5/565—Preheating of scrap
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/08—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
    • F27B3/085—Arc furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
    • F27B3/18—Arrangements of devices for charging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
    • F27B3/18—Arrangements of devices for charging
    • F27B3/183—Charging of arc furnaces vertically through the roof, e.g. in three points
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
    • F27B3/18—Arrangements of devices for charging
    • F27B3/183—Charging of arc furnaces vertically through the roof, e.g. in three points
    • F27B3/186—Charging in a vertical chamber adjacent to the melting chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/10—Details, accessories, or equipment peculiar to hearth-type furnaces
    • F27B3/20—Arrangements of heating devices
    • F27B3/205—Burners
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D11/00—Arrangement of elements for electric heating in or on furnaces
    • F27D11/08—Heating by electric discharge, e.g. arc discharge
    • F27D11/10—Disposition of electrodes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D13/00—Apparatus for preheating charges; Arrangements for preheating charges
    • F27D13/002—Preheating scrap
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/0024—Charging; Discharging; Manipulation of charge of metallic workpieces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/0025—Charging or loading melting furnaces with material in the solid state
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D2003/0034—Means for moving, conveying, transporting the charge in the furnace or in the charging facilities
    • F27D2003/0038—Means for moving, conveying, transporting the charge in the furnace or in the charging facilities comprising shakers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27M—INDEXING SCHEME RELATING TO ASPECTS OF THE CHARGES OR FURNACES, KILNS, OVENS OR RETORTS
    • F27M2002/00—Disposition of the charge
    • F27M2002/11—Continuous charging
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling
    • Y02P10/216—

Definitions

  • the present invention concerns a method for melting metal material in a melting plant which comprises means to feed a metal charge, for example scrap, and non-ferrous material, to an electric arc melting furnace.
  • the invention also concerns the melting plant adopting the method.
  • the present invention is applied in processes for melting metal charge with a substantially continuous loading.
  • Plants for the melting of metal material are known, of the continuous loading type, which comprise an electric arc furnace associated with means to feed the metal charge, which provide to feed the latter through a lateral opening made in the wall or casing of the electric furnace.
  • the electric furnace comprises at least a container, or shell, in which the lateral opening is normally made, and a covering roof.
  • the electrodes are positioned and/or introduced through holes in the roof.
  • the continuous feed means can be the vibrating type to allow the load to advance, and cooperate on one side with the electric furnace and on the other side with a scrap-loading system.
  • the feed means can also be associated with translation means, which translate the feed means to position them in different positions inside the furnace, for example to allow an equal, regular and uniform distribution of the metal charge inside the furnace.
  • translation means which translate the feed means to position them in different positions inside the furnace, for example to allow an equal, regular and uniform distribution of the metal charge inside the furnace.
  • solutions are known in which the end of the feed mean is positioned flush with the inner wall of the furnace, for example during the continuous loading of the scrap, and distanced from it, for example during the tapping step, when the furnace is inclined so as to tap the liquid metal, to prevent problems of reciprocal interference.
  • solutions of the continuous loading type normally use a loading system using baskets, in order to create on the bottom of the furnace a mass of metal material to be melted at start-of-cycle. When this mass has been completely melted, the feed means are positioned and the continuous process of loading the scrap into the furnace is started.
  • the quantity of material introduced with the basket is that necessary to define the so-called “hot heel”, that is, the quantity of liquid metal that is always kept inside the container or shell also after tapping.
  • tap-to-tap the time between one casting and the next is called “tap-to-tap”.
  • steps are provided in which electric power is supplied, hereafter identified as a “power-on” condition, and non-operating steps, in which no electric power is supplied, indicated as “power-off”. These steps are correlated to the modes of unloading the material into the furnace.
  • the quantity of metal charge inside the furnace is normally correlated to the degree of melting of the scrap inside the electric furnace.
  • the quantity of solid mass loaded is made substantially equal to the quantity of solid material that is melted. In this way, inside the liquid mass there is only a small part of solid mass that is melted on each occasion.
  • the bath of molten steel is kept at a temperature equal to or more than 1560° C.
  • the bath of molten steel is taken to a temperature comprised between 1600° C. and 1650° C. to allow the subsequent tapping operation.
  • the molten steel at these temperatures has high reactivity, due to the high concentration of oxygen in it, and high turbulence due to the high convective motions that take place inside it.
  • the reduction in reactivity of the molten steel is obtained by means of “killing” methods, which provide to add reaction substances inside the bath of steel which react with the oxygen.
  • reaction substances inside the bath of steel requires a determinate reaction time so that the chemical reactions are completed. During this time interval, there is an advance in the process of erosion and corrosion of the refractory walls of the furnace.
  • the high temperature at which the liquid steel is maintained allows to promote the advance of the chemical reactions exponentially, but has the disadvantage that there is a considerable increase in the deterioration of the refractory covering the furnace.
  • auxiliary energy supply means such as for example combustible gas burners, which are disposed on the walls of the furnace and which provide to heat the load of scrap introduced into the furnace.
  • the energy supply means can also be suitably disposed to generate an injection of oxygen at high speed, which penetrates through the layer of slag and into the molten metal, and increases the supply of heat energy to the bath thanks to the exothermic oxidation reactions of the alloy elements of the iron.
  • the energy supply means must however be disposed at a determinate distance from the metal bath in order to preserve their integrity with respect to deteriorating agents such as the very high temperature, the splashes of slag and/or molten metal. This means that they lose efficiency.
  • the flame of the energy supply means has a very low yield when they are associated with a functioning process with a flat bath.
  • the interaction of the flame, which is highly turbulent, with the surface of the bath protected by slag, can alter the correct metallurgic practice during melting.
  • U.S. Pat. No. 5,654,976 A discloses a method for melting ferrous scrap metal in a submerged arc furnace.
  • the arc strikes between the electrode and the bath, and not between the electrode and the metal charge, as happens in the furnaces above discussed.
  • the furnaces with a submerged arc are only used to obtain oxides or iron alloys, and not steel.
  • U.S. Pat. No. 5,654,976 A does not provide any arrangement to reduce the wear of the refractory that, in any case, requires a completely different approach since, as we said before, the technology that uses a submerged arc needs completely different requirements than the technology of the “uncovered” arc.
  • U.S. Pat. No. 6,693,948 B2 discloses an apparatus and a method for arc-melting cold iron source which provides to maintain an amount of charge in the furnace and in the pre-heating shaft even after the tapping of the melted steel.
  • the solution disclosed in this document has the disadvantage that an amount of cold charge made of scrap is maintained also during the tapping of the liquid steel; this has the shortcoming to contaminate the liquid steel with the scrap and does not allow to perform a careful metallurgical control of the melted product.
  • One purpose of the present invention is to perfect a method and obtain a corresponding plant for melting metal material that is efficient and that allows to optimize and reduce the electric power required for melting.
  • Another purpose of the present invention is to reduce the losses of heat energy from the bath of molten metal.
  • Another purpose of the present invention is to reduce the effects of wear on the walls of the electric furnace and therefore the maintenance interventions thereon, with the advantage of improving the overall productivity of the plant.
  • Another purpose of the present invention is to allow to use alternative and auxiliary forms of power other than electric, with high efficiency.
  • the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
  • a method for melting metal material according to the present invention is performed in a melting plant that comprises at least an electric furnace having a container or shell into which the metal material is introduced, for example scrap of various sizes, and feed means to load, possibly continuously, the metal material into the shell.
  • the method comprises at least a loading step, possibly continuous, of the metal material into the shell by means of the feed means, a melting step in which the metal material is melted, and a subsequent tapping step in which the metal material is tapped.
  • At least a first substep is provided, in which the metal material is loaded inside the shell with a big load in terms of mass over the unit of time, so as to generate a correspondingly big accumulation of solid material inside the shell, and at least a subsequent second substep in which the quantity of metal material unloaded into the shell is regulated so as to maintain, inside the liquid bath that is gradually formed, a quantity of solid mass substantially equal to the quantity of metal material that defines said accumulation.
  • the feed means are governed by a control device that is suitable to regulate the quantity of metal material loaded.
  • containing the temperature of the molten metal also allows to perform a killing action on the steel which reduces its reactivity. In this way it is possible to further reduce the wear on the walls of the shell, and also to improve the quality of steel obtained.
  • the quantity of solid metal material that defines the accumulation is comprised between 25% and 45% of the overall quantity of molten material tapped.
  • the quantity of solid metal material that defines the accumulation is comprised between 30% and 40%, preferably between 32% and 38%.
  • the feed means are disposed at the side and above the shell, and the metal material that defines the accumulation is disposed at a height near the feed height of the feed means.
  • the feed means can comprise a conveyor, possibly associated with vibration means which, by means of positioning means, is disposed in proximity to one edge of the shell for loading the metal charge.
  • an accumulation is defined that protrudes with respect to the level of material that is melted on each occasion.
  • a third substep is provided during which the feed load is reduced until it is canceled, namely the loading process is stopped, to allow all the metal material present in the furnace to be completely melted.
  • the process of tapping takes place only when the whole solid mass has melted, so as to ensure an excellent metallurgical control of the steel, ensuring the absence of contamination by solid scrap.
  • the method also provides that, during the tapping step of the molten material from the shell, a determinate level of molten material is left, also known as the hot heel, which makes it possible to quickly restart a subsequent melting step.
  • the level of the hot heel unlike what normally happens in the state of the art, is substantially halved, and in particular is comprised between 10% and 25% of the molten material present in the shell before the tapping step. This allows to increase the overall productivity of the plant.
  • auxiliary heat energy is provided, by means of heating means of the combustion type, such as for example gas burners. In this way it is possible to further increase the heat energy for melting the metal material.
  • the energy supply means are disposed in proximity with the accumulation of solid material to increase the temperature of the metal material just unloaded into the furnace.
  • the particular disposition allows to direct the flame of the energy supply means and put it into direct contact with the accumulation of metal material so as to provide an efficient heating thereof.
  • the accumulation of metal material functions as a barrier against possible splashes and against the high temperatures of the molten material that could affect the energy supply means. This allows to increase the working life and reduce the maintenance interventions on the energy supply means.
  • the present invention also concerns a plant that performs the method for melting metal material as described above.
  • FIG. 1 is a graph showing the trend of the functioning parameters of a continuous loading melting furnace, using a state-of-the-art method as described above;
  • FIG. 2 is a graph showing the trend of the functioning parameters of a continuous loading melting furnace, using a method according to the present invention
  • FIG. 3 is a schematic representation in section of a melting plant
  • FIG. 4 is a plan schematic representation of FIG. 3 ;
  • FIG. 5 is a part view of a plant that uses a method according to the present invention.
  • a melting plant for metal material is denoted in its entirety by the reference number 10 and comprises at least an electric arc furnace 11 which is served by feed means 12 to feed a metal charge, such as for example scrap S ( FIG. 3 ), suitable to move the latter according to a determinate axis of feed Z.
  • a metal charge such as for example scrap S ( FIG. 3 )
  • the scrap S is loaded in a known manner onto the feed means 12 , and has a determinate size that can even vary greatly.
  • the furnace 11 comprises, in its essential parts, a container or shell 13 and a roof 15 disposed above and to cover the shell 13 .
  • Three holes are made in the roof 15 , to house and/or position three electrodes 16 , which are suitable to generate an electric arc in the metal charge present in the shell 13 .
  • the roof 15 and the electrodes 16 are associated with lifting and rotation devices 24 , which are suitable to lift the roof 15 and the electrodes 16 , even independently of each other.
  • the shell 13 ( FIG. 5 ) is provided with a bottom, or sole 36 , and a lateral wall 37 , also called upright, both made of refractory material so as to resist the high temperatures that are reached during the melting step, and the highly reactive environment.
  • the shell 13 has a depth D ( FIG. 5 ) that determines the maximum quantity of liquid metal and possibly slag that can be contained inside it.
  • the shell 13 ( FIG. 5 ) is mounted on supports (not visible in the drawings), and actuation means 28 are provided to rotate the shell 13 around a determinate axis of rotation C.
  • the axis of rotation C is disposed substantially aligned or in direct proximity with the axis of feed Z of the feed means 12 .
  • the furnace 11 also comprises a panel 22 provided with a lower edge 28 disposed resting on the upper edge of the shell 13 .
  • the panel 22 develops substantially in progression with the walls of the shell 13 and above it the roof 15 is disposed, in order to close the shell 13 .
  • the shell 13 and the panel 22 in proximity to their common connection edges, comprise sealing means, not visible in the drawings, conformed to prevent heat dispersions and/or leakages of the fumes.
  • the panel 22 is provided with an opening 17 through which the feed means 12 are positioned, to feed the scrap S.
  • the feed means 12 are disposed with their discharge edge substantially flush with the wall of the panel 22 and the shell 13 .
  • the height of the panel 22 is correlated to the entity of the opening 17 , which in turn is sized according to the feed means 12 or the delivery of scrap S fed by the feed means 12 .
  • the conformation and disposition of the opening 17 in the panel 22 is also determined in relation to the movements to which the shell 13 will be subjected during the casting process.
  • the opening 17 is disposed so as to respect the condition of alignment or substantial alignment between the axis of rotation C of the shell 13 and the axis of feed Z of the feed means 12 .
  • This condition allows to perform tapping of the molten metal, or slagging, without requiring that the feed means 12 be retracted. This reduces the process times since, as soon as the tapping is finished, it is possible to start the loading operations without having to wait for the electric arc to be switched on.
  • the opening 17 is made distanced with respect to the lower edge 28 of the panel 22 by a determinate height F which, in some embodiments, is comprised between 0.3 and 3 times the depth D of the shell 13 , preferably between 0.5 and 2.5, more preferably between 0.5 and 1.5.
  • the portion of panel 22 comprised in the height F has the function of containing the scrap S loaded by the feed means 12 , as will be described in more detail hereafter.
  • Heat exchange means in this case exchangers with a bundle of tubes such as cooling panels, are associated with the panel 22 and the roof 15 , to guarantee their mechanical resistance even at high temperatures.
  • the feed means 12 are suitably conformed to allow the shell 13 to rotate, both during tapping and during slagging, preventing conditions of interference.
  • the feed means 12 ( FIGS. 3-5 ) comprise a conveyor 14 of the vibration type that provides to move the scrap S forward toward the shell 13 with a determinate load Q, which selectively varies according to process parameters which will be described hereafter.
  • the conveyor 14 has a substantially trapezoid transfer section with a flat bottom 40 and the end from which it unloads the scrap S is disposed at a determinate distance E from the lower edge of the opening 17 ( FIG. 5 ).
  • the bottom 40 can also be concave toward the surface containing the scrap S.
  • the terminal part of the conveyor 14 is mounted on a trolley served by vibration devices 23 ( FIG. 5 ) and by a positioning device 25 , only partly shown in the drawings.
  • the positioning device 25 in this case a hydraulic actuator, is suitable to move the trolley and with it the conveyor 14 , from and to the opening 17 of the panel 22 in order to unload the scrap S into the shell 13 .
  • the conveyor 14 can be translated in a horizontal direction to and from the furnace 11 , it is always located at the same height with respect to the shell 13 .
  • the conveyor 14 or possibly the vibration devices 23 , are controlled by a control device 27 ( FIG. 3 ), which is suitable to regulate the load Q of the scrap S that is conveyed to the shell 13 and introduced therein.
  • feed means such as for example conveyor belts.
  • Auxiliary energy supply means 20 in this case burners, are mounted in the panel 22 , between its lower edge 28 and the lower edge of the opening 17 , with the function of further supplying heat energy.
  • burners 20 ( FIG. 4 ), four in this case, are associated with the panel 22 near the side where the scrap S is unloaded and are disposed substantially near the center line of the height F.
  • Oxygen injection means 21 are also provided in a known manner, suitable to inject oxygen into the bath of steel to allow to eliminate unwanted elements from the composition of the liquid.
  • the melting method according to the present invention provides a step of starting the plant 10 in which the feed means 12 load the furnace 11 , distributing the scrap S uniformly on the bottom or sole of the shell 13 .
  • the start-up step can also be performed with a basket as described in the state of the art.
  • the roof 15 and the electrodes 16 are raised with respect to the shell 13 and displaced laterally to allow access for the basket.
  • the roof 15 is used to close the shell 13 , the electrodes 16 are positioned and inserted through the holes made in the roof 15 , and the melting of the metal charge therein is started, to generate a determinate level of hot heel H ( FIG. 3 ) of the molten metal which in this case is substantially equal to the level of the hot heel H that will be subsequently kept from tap-to-tap.
  • a level of hot heel H will be maintained inside the shell 13 which is comprised in a range between about 10% and 25% of the total quantity of liquid metal present before tapping.
  • the method Following a tapping step of the molten metal, that is, immediately after the tapping step, the method provides a step of continuous loading of the scrap S, a simultaneous or at least partly simultaneous step of supplying electric power to the electrodes 16 , power-on condition, and therefore a consequent step of melting the metal charge.
  • the feed means 12 are configured to remain in the work position also during the tapping or slagging step, and as soon as one of these steps has come to an end, the feed means 12 can immediately re-start feeding the furnace 11 , thus preceding the power-on condition.
  • the supply of electric power is interrupted, in a power-off condition, and the tapping or casting step is provided.
  • a first substep 31 is provided ( FIG. 2 ), during which the scrap S ( FIGS. 3 and 4 ) is loaded inside the shell 13 with a big load so as to generate, at least near the opening 17 , an accumulation 30 of solid mass of scrap S.
  • the accumulation 30 defines a mass of solid material that is disposed at a height near that of the opening 17 , that is, almost flush with the bottom 40 of the conveyor 14 .
  • the first substep 31 provides that the feed means 12 supply the furnace 11 with a specific load of scrap comprised between about 50 (kg/min)/MW and about 150 (kg/min)/MW, preferably about 100 (kg/min)/MW.
  • the load Q of scrap S is comprised between about 3000 kg/min and about 9000 kg/min, preferably between 6000 kg/min and about 7000 kg/min.
  • the load Q of scrap S is maintained for about 10%-20%, preferably about 13%-17%, of the time comprised between power-on and power-off, in this case about 6 minutes.
  • the load Q of scrap S is regulated by the control device 27 associated with the conveyor 14 .
  • the melting of the metal is also started—power-on condition.
  • the melting of the metal is started with a delay of about 2 minutes from the first substep 31 .
  • a second substep 32 is provided, during which the load Q of scrap is reduced, to allow the electrodes 16 to melt the metal, substantially in coordination with the quantity of scrap S that is introduced by the conveyor 14 .
  • the load Q of scrap S is regulated so as to maintain in the liquid bath of steel a quantity of solid mass of scrap comprised between 25% and 45%, preferably between 30% and 40%, even more preferably between about 32% and about 38% of the overall quantity of liquid metal that will later be tapped.
  • the specific load of scrap S is kept substantially constant between about 75 (kg/min)/MW and about 85 (kg/min)/MW.
  • the load Q of scrap S is comprised between about 4500 kg/min and 5000 kg/min.
  • the balanced condition between the mass of scrap that is fed and the quantity of solid mass that is melted is maintained for a duration of about 10%-20%, preferably about 13%-17%, of the time comprised between power-on and power-off, in this case about 13 minutes.
  • the solid mass contained inside the liquid steel functions as a heat accumulator, also called “thermal flywheel”, and allows to keep the steel already melted at a temperature lower than that it reaches in the state of the art.
  • molten steel at a lower temperature allows to keep the bath in a condition of stability so as to reduce phenomena of wear on the walls of the shell, and hence to reduce the frequency of maintenance operations to restore them.
  • the load Q of scrap is reduced, in this case initially halved, and is then substantially interrupted or in any case kept at a minimum level. In this way the whole solid mass present in the liquid is allowed to melt.
  • the load is definitively stopped and all of the solid metal has passed to the liquid state.
  • a step of overheating the liquid steel is also provided, in a known manner, to determine the desired thermal and chemical characteristics of the bath of molten metal.
  • the burners 20 heat the scrap S directly, with a direct flame.
  • the accumulation 30 of scrap S at least during the second substep 32 , has a substantially constant height and therefore functions as a barrier against possible splashes, or against the high temperatures of the liquid metal, allowing both to increase the working life and also to bring the burners 20 nearer to the solid accumulation mass 30 ; all this gives the advantage respectively of a reduction in the maintenance times required for, and efficiency of, the burners 20 .
  • operations to inject oxygen are provided with the functions as described above, operations to supply carbon to moderate the production of iron oxide, and operations to supply lime and magnesite to modify the composition of the slag and enable the dephosphorization process.
  • additives are added to promote the increase in volume of the slag, also known as slag foaming, which has the effect of protecting the bath of metal from oxidation, and also shielding the heat irradiation energy generated by the molten bath and the electric arcs of the electrodes 16 .
  • the supply of electric power is interrupted, power-off condition, there is a step of tapping the molten steel by means of inclination, also known as tilting, of the shell 13 .
  • the tapping step provides to rotate the shell 13 until the determinate level of hot heel H, as identified above, is left inside it.
  • the furnace 11 allows to keep a larger volume of slag, in that it does not overflow from the opening 17 used for loading scrap S.
  • the tapping hole is closed and the shell 13 is returned, by rotation, to its normal position.

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  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Vertical, Hearth, Or Arc Furnaces (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
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JP6203376B2 (ja) 2017-09-27
WO2014174463A2 (en) 2014-10-30
RU2015149935A (ru) 2017-05-26
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CN105612398A (zh) 2016-05-25
MX2015014824A (es) 2016-06-21
RU2639078C2 (ru) 2017-12-19
MX366349B (es) 2019-07-05
WO2014174463A3 (en) 2015-02-26
ITUD20130052A1 (it) 2014-10-24
EP2989402A2 (en) 2016-03-02

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